A heat transfer medium composition which contains a glycol or an alcohol as its main component and a variety of corrosion inhibitors are mainly used in cooling systems for internal combustion engines, solar systems, floor heating systems, air conditioners and the like.
There exists a conventional heat transfer medium composition used in cooling systems for internal combustion engines which contains a glycol as its main component as well as an alkyl benzoate or its alkali metal salt, ammonium salt or amine salt, aliphatic monobasic acid of C8 to C12 or its alkali metal salt, ammonium salt or amine salt, and hydrocarbon triazole (Japanese Patent Publication H4 (1992)-42477).
However, glycols and alcohols which are used as a main component of such heat transfer medium compositions contact oxygen in use at a high temperature and high pressure, and are therefore oxidized, though lightly, and gradually converted into an acid such as glycolic acid.
Oxidation of these glycols and alcohols progresses as used continuously, and the pH value of the heat transfer medium gradually lowers from the originally set value of pH 6 to pH 10, progressively corroding the metal parts of cooling systems.
In addition, metals used in cooling systems, solar systems, floor heating systems or air conditioners such as aluminum, aluminum alloys, cast iron, steel, brass, solder and copper gradually dissolve into the heat transfer medium as metal ions. The eluted metal ions react with the corrosion inhibitor in the heat medium, forming precipitation. As a result, the remaining amount of the effective corrosion inhibitor in the heat medium is reduced, and the pH value of the heat medium is lowered below the effective working range, further inducing metal corrosion.